This paper analyzes grasp stability of two objects in two dimensions. In the previous researches on the grasp stability, the number of grasped objects is restricted to 1. For efficiency of tasks, multiple objects had better been grasped and manipulated by a robot hand. In order to design stable grasp, grasp stability of multiple objects must be quantitatively evaluated. In case of two grasped objects in two dimensions, the number of parameters of object displacement is 6. However, the displacement of the objects is constrained by each other, because the contact between the objects must be maintained. Independent parameters of the object displacement are provided and then finger displacement is derived. The grasp stability is evaluated from the viewpoint of the potential energy method. From numerical examples, the effect of curvature at contact point between two objects is demonstrated. The effect of this curvature stands for the feature of multiple objects.